While the fundamental duty of engine coolants has not changed they must transfer excess heat and offer freeze and boiling protection, plus corrosion and liner protection modern coolants must transfer more heat than in the past, largely due to new emissions systems.
When considering the energy consumed to power a heavy-duty diesel engine, remember that only about one-third goes to the drivetrain; another 30% is lost as heated exhaust and 7% is radiated from the engine, according to Regis Pellet, director of coolant technical service and development at Old World Industries. The remaining 30% of energy heat must be removed by the engine’s coolant and cooling system.
“Without efficient cooling, engine components, seals and gaskets and lubrication will age rapidly, wear down prematurely and fail,” Pellet says. “It is the coolant’s job to keep all engine components operating within the temperature range for which they have been designed. In addition to the coolant’s number one job of heat removal, a coolant also must provide freeze protection for the winter months and corrosion protection of all cooling system components year-round.”
Engine technology has advanced over the past decade to include additional components for emission compliance. Jeff Snyder, industrial brand specialist for Chevron Lubricants, says some of these technologies, such as exhaust gas recirculation (EGR), can add upward of 30% more heat into the cooling system, thermally stressing the coolant technology.
“With EGR, hot exhaust gases are recycled to the engine’s combustion chamber, diluting the diesel fuel/air mixture and reducing NOx production,” Pellet says. “All the added heat associated with the recycled exhaust must be removed by the coolant through an EGR cooler…coolants must be thermally stable while still providing excellent corrosion protection under these more demanding conditions.”
“In order to meet fuel economy and emission requirements, heavy-duty OEMs are increasing power densities using turbo chargers, inner coolers, high efficiency aluminum radiators, and multiple cooling system loops to provide the necessary cooling,” explains Stede Granger, OEM technical services manager for Shell Lubricants.
He adds that since these engines and cooling systems contain a significantly greater amount of aluminum, it has been observed that nitrite-containing coolants may react with aluminum components, causing unwanted reactions that can damage aluminum components. Shell says its new HD ELC coolants are nitrite-free and provide greater aluminum protection.
“For the emission technology, most OEMs are using a combination of SCR and EGR of which both strategies are increasing the additional thermal load on the coolant,” Granger says. “To meet these challenges, Shell’s HD ELC coolants are also formulated with greater oxidation and thermal stability.”
According to Josh Hahn, Cummins Filtration coolants and chemicals business manager, in addition to engine cooling, the engine maker uses coolant to cool EGR coolers, turbochargers, hydrocarbon injectors and DEF doser valves. “Cummins coolant recommendations have evolved over time to reflect changes in diesel engine and coolant technology, environmental regulations and customer needs.
Since 1995, Cummins has recommended the use of only fully formulated coolants meeting ASTM D6210, TMC RP 329 (ethylene glycol) and RP 330 (propylene glycol) specifications. However, Cummins discovered significant weaknesses in some coolants meeting these ASTM specifications. This led to the development of Cummins Engineering Standard 14603 to ensure coolant used in Cummins engines meets the requirements of all engine components.”
Generally speaking, the main types of engine coolants are conventional (inorganic), organic additive technology (OAT), and hybrid.
“Both (conventional and OAT) technologies can provide excellent, proven corrosion protection when used and maintained properly,” advises Old World’s Pellet. He notes that conventional coolants protect against corrosion by coating all surfaces with a protective layer of inorganic oxides, such as silicate or phosphate layers. “This layer works well, but inhibitors are consumed in the process of layer formation, so conventional heavy-duty coolants must be refortified with supplemental coolant additives (SCA) in order to maintain effective corrosion protection over the life of the heavy-duty diesel engine.”
Inorganic additives need to be replenished at routine maintenance intervals to ensure proper function and protection, according to Chevron’s Snyder, who says this can be done through either liquid additions or water filters that contain the additives.
Pellet says conventional coolants should typically be replaced entirely after two to three years of use or 200,000 to 300,000 miles.
OAT coolants, conversely, do not rely on protective layering. “OAT inhibitors react only where needed at the sites of potential or incipient corrosion,” Pellet explains. “Thus, inhibitor consumption is greatly reduced so that SCA addition is no longer required. A one-time addition of an extender is sometimes required at half life, typically after 300,000 miles of use, effectively doubling the lifetime of OAT coolants.”
He adds OAT coolants can last for 600,000 to 1 million miles and often are referred to as “extended life coolants.” The reduced maintenance and improved cooling properties are key advantages to OAT coolants and most major engine manufactures offer OAT coolant as a factory fill option.
Extended life technology also offers increased heat transfer capabilities, since the additive technology does not create another barrier layer to heat transfer, notes Chevron’s Snyder.
Hybrid coolants use a mixture of inorganic and organic additives to provide buffering, corrosion protection and liner pitting, notes Cummins’ Hahn, who adds that recent advancements in engine and cooling system technology have resulted in more OEMs moving to a full OAT type coolant.
Because of the first and foremost coolant function efficient heat transfer almost all coolants contain 40% to 60% water, which is “the most effective heat transfer agent readily available for this number one job,” says Old World’s Pellet. “Where heat transfer is limiting, even higher levels of water may be used.”
Most coolants today also offer freeze protection, which is provided by ethylene glycol. “When mixed with water, glycol can lower the coolant freeze point to -30? to -50? F with the greatest freeze point depression coming at about 60% glycol content,” Pellet explains. “Glycol is not as efficient at heat transfer as water, so some cooling capability is sacrificed to gain freeze protection.”
The third component is comprised of a corrosion inhibitor package. Corrosion inhibitors must protect all cooling system components, which can include iron, steel, copper, brass and aluminum. “While of great importance, the inhibitor package may comprise only 3% to 5% of the total coolant composition,” Pellet says, adding that coolant also contains minor components such as scale inhibitors, anti-foams, dyes and sometimes bittering agents to reduce chances of accidental ingestion.
According to Mike Tourville, director of marketing for Evans Cooling Systems, because of newer engine technologies, a coolant that can transfer heat under extreme environments without forming vapor and hence pressure or overheating is a preferable choice. Water loses most of its heat transfer abilities when it turns to vapor, creating stress within the cooling system. A waterless coolant, such as Evans, does not form vapor in an engine because of its high boiling point.
“Water-based coolants are pushed to their limits and the demands of an engine are forcing cooling technologies to raise the bar,” he notes. “One major difference between water-based coolants and Evans waterless coolants is that the bar can be raised without worrying about cooling system failure.”
Tourville explains that water’s low boiling point normally at 212-degrees F, but up to 240- to 250-degress in a pressurized system becomes the failure temperature of the cooling system. Coolants containing 50% water (most coolant is a 50/50 mix with ethylene glycol and water, along with anticorrosive additives) will be much more likely to overheat.
“Evans waterless coolant, by contrast, doesn’t boil until 375-degrees F,” he says. “That separation of the operating temperature and the higher boiling point provides a safe margin without the worry of overheating.”
Because of Evans waterless coolant’s higher boiling point, vapor will not be formed, resulting in less stress on the cooling system. “Normally, a cooling system operates under 15 lbs. of pressure,” Tourville explains.
“Evans waterless coolant might normally operate at about 3 lbs. Evans will not prevent leaks, but can make them much less likely to occur with the lower pressure.”
Evans’ higher boiling point enables an engine to take advantage of a temperature range that water-based coolants cannot handle, he says, adding this translates into fuel savings by allowing greater efficiency within the cylinder and enabling a reduction of fan-on time. Typically, a truck converted to Evans will see a fuel economy improvement between 3% and 8%, Tourville notes.
Evans waterless coolant also essentially eliminates cavitation erosion of the cylinder liner, ultimately reducing maintenance costs. According to Tourville, a John Deere Cavitation test performed at Southwest Research Institute demonstrated that Evans performed 70% better than the next best-tested coolant to avoid cavitation erosion.
Estimates project up to 40% of total engine costs are related to problems that originate in the cooling system, according to Hahn at Cummins. Repairs are costly and create unnecessary downtime that affects equipment operations and customer deadlines.
Know your coolant colors
Shell Lubricants reminds that TMC has established recommended coolant colors for different types of coolants, though the colors are not required and not all manufacturers follow the recommendations.
The colors that are recommended are red for extended life coolant (ELC), purple/pink for fully formulated ethylene glycol-based coolant, blue for fully formulated propylene glycol-based coolant, and green for conventional coolant. Shell said it generally follows the color recommendations; however, yellow is used for its nitrite-free coolant, Shell Rotella Ultra ELC.
“While coolant color is a helpful guide, the most important thing to know is the type of coolant you have in your truck and to not mix coolant types,” says Shell’s Stede Granger, OEM technical services manager. “Each type of coolant is different and needs to be maintained in a different way.”
He adds this is particularly important for both conventional fully formulated and ELCs, which can be contaminated if they are diluted with other types of coolants. Mixing of conventional fully formulated coolant and ELC reduces the effectiveness of the corrosion inhibitor in both products and the poorest corrosion inhibitor will dictate the performance.